In many jurisdictions, the law requires that trucks and trailers used in the transport of various materials such as sand, gravel, grain, trash and other loose substances have a cargo area fully covered by a tarpaulin sheet or a net in order to prevent transported material from being blown away and causing driving hazards for following vehicles or from dumping litter on the highway.
Contractible canopies are usually rolled up or bundled up when not in use against the forward edge of a cargo area, then deployed on command until the leading edge of the canopy meets the trailing edge of the cargo compartment.
Because the framework holding the tarpaulin tends to ride a few centimeters above the top edges of the container, a gap may be left between the leading edge of the tarpaulin and the back of the cargo area. This gap can allow material to pass through and be dumped on the highway. The problem has been addressed in the prior art with rather complex and bulky mechanisms as disclosed in U.S. Pat. No. 4,740,029 Tuerk; No. 5,524,953 Shaer; and No. 6,007,138 Cramaro. These three patents are hereby incorporated herein by this reference into this specification. The multiplicity of levers, pulleys, push-rods, and articulations in the embodiments of the prior art increase the chances of failure and require frequent maintenance, especially if the vehicle, as is often the case, operates in a very dusty environment.
The instant invention results from an attempt to provide a simple, foolproof and dust-proof closure at the back edge of a contractible canopy covering a container.